backup problem

I have created a backup file of my documents on the command line using
tar utility. Now, I want to update the file periodically without
creating the backup file of all the documents again from the
ground-up. How do I update the backup file using tar?
Name of the file: docs_backup.tar.bz2
Destination: /home/bb/Public
Source path: /media/d
For backing up which method is better? tar utility or a gui
application? If gui application, what is the name?